Electrocardiograph



March 20,1956

Filed March 23, 1950 R. H. KRUSE ELECTROCARDIOGRAPH 2 Sheets-Sheet 1lNVENTOR Ralph E Kruse BY M Mr (1 ATTORN 2 Sheets$heet 2 R. H. KRUSEELECTROCARDIOGRAPH March 20, 1956 Filed Mal ch 25, 1950 m mm INVENTOR rg, ATTORNE .4!

Ralph [i Kruse BY M United States Patent C ELECTROCARBIOGRAPH Ralph H.Kruse, Pclham, N. Y., .assignor to Cambridge Instrument Company, Inc.,New York, N. Y.

This invention relates to electrocardiographs or like instruments, andmore in particular to electrocardiographs of the direct writing typewhere electrocardiograms are made by the direct contact of a stylus withthe record sheet.

It is an object of the present invention to provide an improvedarrangement for making records on instruments of the above-mentionedtype. Ordinarily, such an instrument has a suspended recording arm orwriting boom which may bea pen or other writing instrument, or a stylus,and is formed by an elongated boom portion carrying the recording orwriting element, for example, a stylus element, on its projecting end.Some such prior type instruments trace a record on curved ordinateshaving a radius .of curvature dependent upon the effective length of theboom. Records of this character, having the arcuate form'of the curvedordinates, are objectionable; first, because the records are confusingand are difficult to read and interpret; and, second, especially in thecase of-electrocardiograms and the like, because the records take on acharacter different from those previously known and, therefore, appearunfamiliar to the technicians interpreting them.

Records of this type have also been produced on rectilinear coordinates,by passing the paper over a knife edge and then swinging therecordingelement through an are which is intersected by the paper at the knifeedge so that the recording element marks the paper where it crosses theknife edge.

But this introduces a tangential error which in itself is undesirable,but becomes quite objectionable because it is not apparent and,therefore, the technician will be influenced toward misinterpretation ofthe record. Although records of this general nature have been producedwith rectangular coordinates with a straight line movement of therecording element, the arrangements for accomplishing this have been socomplicated as to be impractical and they have other characteristicswhich interfere with their wide use. It is an object of the presentinvention to avoid the various difiiculties, such as those referred toabove, which have been encountered in the past with records of thisgeneral character. It is a further object to provide apparatus of theabove character which is sturdy in construction, accurate and dependablein accomplishing the desired result, light in weight, and inexpensive tomanufacture and maintain; and, which is adaptable to meet the needsarising from special circumstances in this particular field.

In accordance with the present invention, an arrangement is provided forproducing records of the above character on truly rectangularcoordinates. The illustrative embodiment of the present invention is anelectrocardiograph having a recording galvanometer which swings a styluson the end of a boom through an arc across the width of a strip ofmoving paper. With this arrangement an accurate rectangular coordinatecharacteristic is obtained by curving the record paper in a cylindricalsurface, the ax s f h c co nc d ith he s n i 2,739,030 Patented Mar. 20,1956 of the stylus, which is the axis of rotation of the galvanometercoil. The paper at the zone of recording has a predetermined radiuswhich is a fixed characteristic of the instrument.

The cylindrical curving of the paper in this accurate manner is obtainedby drawing it across and in contact with the concave surface of a curvedplaten having the desired curvature and a fixed relationship withrespect to the axis of the galvanometer coil. The recording element orstylus contacts the paper along an arc of the cylinder to which thepaper is conformed by the platen and which, as indicated, has its axiscoincidental with that of the galvanometer coil and the swinging axis ofthe stylus which is fixed thereto. In the illustrative embodiment, theboom which supports the stylus is straight and extends diagonally fromthe coil, but that arrangement is not essential to certain aspects ofthe invention. The stylus is pressed against the paper with sufiicientpressure to produce optimum recording.

Although in this specification and the accompanying drawings l haveshown and described a preferred embodiment of my invention and havesuggested various modifications thereof, it is to be understood thatthese are not intended to be exhaustive nor limiting of the inventionbut on the contrary, are given for purposes of illustration in orderthat others skilled in the art may fully understand the invention andthe principles thereof and manner of applying the same in practical useand be enabled to modify and adapt it in various forms each as may bebest suited to the conditions of a particular use.

In the drawings in which like reference characters refer 1 to like partsthroughout;

Figure l is a fragmentary and somewhat diagrammatic perspective view ofone embodiment of the invention;

Figure 2 is a typical electrocardiogram produced upon the apparatusof'Figure 1;

Figure 3 is a vertical section with certain parts shown in full of theapparatus of Figure 1 ;and,

Figure 4 is a sectional view on the line 4-4 of Figure 3.

Referring particularly to Figure 3 of the drawings, there is shown atthe left a roll 2 of the strip of chart or record paper 4 upon which theelectrocardiograms are produced (see also Figure 1). This paper has acoated recording upper surface, which is white with longitudinal andtransverse markings -(see Figure 2), and is of such a character that ablack line is produced if a heated stylus is moved in contact with thissurface. The coatingacts somewhat as a lubricating medium and littlepressure is required to make the heated stylus produce its marking;thus, the friction between the stylus and the paper is extremely small.Positioned somewhat directly above (Figure 3) the roll of paper is thegalvanometer coil 6 which is supported in a manner to be more fullydescribed below, and which has fixed to it a recording boom 8 whichextends diagonally downwardly to the paper and has a stylus 10 fixed toits lower or recording end.

As shown at the right in Figure 3, the strip of paper 4 is drawn fromthe roll 2 which is mounted in a well in a base plate 3 by a main feedroller 12 against which it is held by a pressure roller 14. Positionedbetween the roll of paper 2 and the feed rollers and resiliently mountedon base plate 3 is a platen assembly 16, formed by a lower platen 18(Figure l) and an upper platen 19. Platen 18 presents a concave surface20 having the curvature of a cylinder the axis of which is coincidentwith the axis of rotation of the galvanometer coil 6. The strip of paper4 is drawn along this surface 20 parallel to that axis and is caused toconform to the curvature of this surface by an arcuate lip 24 on theupper platen 19 which rides against the paper. This lip cooperates withplaten 18 tea, in effect, form a slot through which the paper is guidedwithout being subjected to pinching or restraining pressuresand thecurvature of the paper is determined by the curvature of the lowerplaten. v

The-upper platen 19 is resiliently mounted onthe lower platen so that itis urged toward the position shown, although it can belifted for thepurpose of threading the paper through the platen assembly. Theresilient mount ing is provided by a spring bracket 21 which isgenerally U-shaped in a horizontal plane and'is clamped to the topsurface of the upper platen by a pair of screws 22 (see also Figurie4).The two legs of this spring bracket project parallel to and are spacedfrom the top surfaces of the side portions of the lower platen 18, andthe ends'of these legs extend downwardly and are clamped to the lowerplaten by screws 23. Bracket 21 has sufiicient resiliency to hold'theupper platen. in the position shown and yet this platen may be liftedwith ease so that the strip. of paper 4 can be pushed through alongsurface 20. Thislifting movement of the upper platen is limited by apair of screws 25 which are threaded into the top of the lower platenand have their shanks projecting loosely through openings in bracket 21.These openings are smaller than the head of screws 25 so that the headsof the screws act as stops to limit the movement of the platen. 'Theupper platen is lifted only when the galvanometer and stylus assembly israised awayvfrom the platen assembly. This lifting operation isperformed by a sheet metal bracket or shield 27 which is clamped at itsbase to the top of the upper platen by screws 22 and which projectsupwardly beneath boom 8.

'Platens 18 and 19 are of plastic but directly beneath lip 24 andembedded in the lower platen 18 is a heatconducting metal strip 26, inthis embodiment of sheet aluminum. Strip 26 extends the width of thestrip of paper 4 and conforms to the cylindrical curvature of surface 20so that it is a segment of a cylinder. As will be explained more fullybelow, strip 26 acts to conduct heat away from the stylus at any timethat the temperature in the vicinity of the stylus tends to becomeexcessive. The upper surface of strip 26 is slightly below the curvedsurface 20 so that leeway. is provided in the vicinity of the lip 24 andthe stylus. However, the leeway is notsuflicient to permit the paper todeviate from the true cylindrical form referred to above.

When the strip of paper is drawn from roll 2 it is in fiat form andlater as it passes between rollers 12 and 14 it is again in flat form.However, during the passage between these two points it is conformed toa cylindrical shape or form so that its recording surface is contactedby stylus while this surface has a true cylindrical form and the axis iscoincident with the horizontal axis of galvanometer coil 6. The paperhas such characteristics that it may be diverted in the manner shown toand from this cylindrical form without buckling or wrinkling. 1

During operation, boom 8 is swungthrough an arc of predetermined limits,due to the action of galvanome'ter coil 6 to which the boom is fixed.Coil 6 is rectangular with its sides positioned within two gaps 29 (seealso Figure 4) in a magnetic core structure formed by a permanent magnet28, two poles 30 and a stationary cylindrical core 32 positioned in thecenter of the galvanometer coil 6. The magnetic core structure thusforms two arcuate gaps in which the two sides of the coil are positionedand are subjected to uniform magnetic fields. Coil 6 is supported(Figure l) by four beryllium copper spring clips 34, 36, 38 and 40 whichare positioned in pairs at the two ends of the coil with each clip beingrigidly attached at one end to the coil and having its other end clampedby a screw 42 to the mounting frame. Each of these mounting clips is aflat strip of beryllium copper bent into an 8 form or curve at itscenter and having its ends extending parallel. One end of each of thesprings is clamped to the coil by a band attachment 44 so that the coilis supported symmetrically at four spaced points. These clips tend tohold the coil in its exact horizontal position as shown, but yet thecoil is permitted to rotate about its horizontal axis.

As shown best in Figure 3 there is positioned within the stationary core32 a mounting sleeve structure 46 formed by a central compression spring48 and two cylindrical end members 59. Each of the end members has anextension 52 which projects into a cylindrical opening or recess in theadjacent end wall of the galvanometer coil 6. The end members areclamped in the position shown byset screws 54 and when these set screwsare loosened spring 4% urges the end members away from each other. Theaxis formed by end extensions 52 is coincident with the axis of coil 6which, as indicated above, is also coincident with the cylinder ofsurface 20 of the lower platen. During assembly the end memhers 5% areclamped in such positions that they contact the coil only by their endextensions which project into the openings in the coil. Thus, asleeve-bearing structure is provided for the coil, the axis of which iscoincident with the axis of the coil and the recording surface. However,the coil is supported and its movementis guided by the four spring clipsas discussed above, and the spring clips supply torsional controlwithout any appreciable side or end components.

Galvanorneter coil 6 is deflected by passing signal currents through itand these currents are passed to the coil (see Figure 1) through clips34 and 36. As has been suggested above, stylus 19 is heated and currentfor heating the stylus is carried by clips 38 and 40. Boom 8 is formedby two beryllium copper tubular struts 56 and 58 which are fixed to coil6 at their upper ends and which support the two ends of the U-shapedstylus 10 at their lower ends. Struts 56 and 58 are reinforced and heldin fixed relationship by three rigid transverse struts 60, 62 and 64which are formed of glass fibers shaped as shown and are coated andcemented with a silicone cement having good-insulation properties.During use, the voltage source for heating the stylus is connectedacross clips 38 and 40 which are electrically connected respectively tostruts 56 and 58 and the heating current flows from clip 38 down throughstrut 56 and thence through stylus 10 and back up strut 58 to clip 40.

As indicated above, a metal shield 27 is rigidly clamped to the upperplaten 19 and projects upwardly beneath boom 8.- This metal shield actsas a lifting handle for the upper platen during the threading of thepaper, but it has the important additional function of acting as amagnetic shield for boom 8. Thus, stray magnetic lines from magnet, 28pass through the shield and are thereby diverted from the zone throughwhich the boom swings. In this way, the electrical current which flowsthrough struts 56 and 58 for the purpose of heating stylus 10 does nottend to cause the boom to move as it would tend to do if this shieldwere not provided.

Referring again to Figure 3, the galvanometer unit is mounted from itstop on ,a rigid metal case '70 which providesrigid support for thegalvanometer unit during use. Case has a main rectangular structurewhich is hinged at the left to the base plate 3 of the instrument by ahinge 72, and at the right the case has an integral forwardly projectingportion which is rigidly held to the base by a releasable clamp 74. Thisclamp has a cam surface latch which tightly engages and firmly holds thecase in place. The case hasa window '76 through which the stylus and thestrip of paper passing under it may be observed. When latch 74 isreleased, the case may be lifted by swinging it counterclockwise inFigure 3 around the pivot formed by hinge 72, and this lifts thegalvanometer unit, and the boom and stylus, away from the platenassembly and the paper. Access may therefore be had to the paper supplyand feed, for example, so that the roll of paper may be renewed and sothat the paper may be threaded. As pointed out above,

during thethreading, the lower edge 24 of the'upper platen may be raisedby pressing on the shield 27.

As shown best in Figure 4, projecting inwardly from the opposite sidewalls of case 70 are two lugs 77, which are in alignment with anvilrecesses in the respective sides of' the lower platen 18. When the caseis swung back down again lugs 77 engage the anvil recesses in theopposite sides of the lower platen 18, and as the latch 74 (-Figure 3')is turned to clamp the frame against the base, these lugs push theplaten assembly down to a predetermined position. Lugs 77 are machinedduring manufacture of the frame so as to have a predeterminedrelationship with respect to the surface upon which the galvanometerunit is mounted, and therefore the galvanometer and the boom and stylusare mounted and adjusted with a predetermined relationship with respectto these lugs. Thus, as the frame swings down to the final positionshown, the lugs cause the lower platen to take a predetermined positionwith respect to the galvanometer coil, and this position is such thatthe paper-conforming surface 20 of the platen has its axis coincidentwith the galvanometer coil axis.

Hinge 72 is clamped to the base plate 3 of the instrument by a screw 78which may be turned by grasping its knurled top end when the case andgalvanometer unit are raised, and by loosening this screw the frame andgalvanometer unit may be removed from its base plate. In view of thefact that the galvanometer unit is the part of the instrument which ismost apt to require testing and service, this arrangement for readyremoval and replacement of the unit has particular advantage.

It has been pointed out above that the recording element is a heatedstylus supported by a boom 8, and that boom 8 is formed by two struts 56and 58 and three transverse struts 60, 62 and 64 which are reinforcingmembers of glass fiber cemented with silicone cement. The heated stylus10 is a hairpin or U-shaped element of electrical resistance wire andits ends project into the ends of the tubular struts 56 and 58 and aresoldered thereto with thin films of solder. The boom with the stylusattached is given a thin gold plate, and it has been found that thisprotects the soldered joints between the struts and the stylus, andinsures longer life. The struts diverge and have their upper endsattached to the galvanometer coil 6 at diametrically spaced points onthe end wall of the coil. While the two struts 56 and 58 have somebending flexibility they are held relatively rigidly in theirlongitudinal extent by the reinforcing struts 60, 62 and 64. Therefore,when the galvanometer coil rotates the boom transmits the movementwithout flexing and the stylus follows the coil movements with greatfidelity. This not only gives improved accuracy of operation but it alsoinsures longer life of the stylus because the stylus and its junctureswith the struts are not subjected to flexing actions.

It has been pointed out above that the heated stylus moves across thesurface of the paper with extremely small friction and, therefore, verylittle force is required to move the stylus. The particular shape ofstylus 10 insures that the stylus will not tend to cut into the paper orotherwise engage the paper in such a way as to interfere with themovement. The particular stylus structure has low momentum and the strutstructure is such as to give maximum strength for operation with minimumWeight. This boom construction and stylus and the spring clips whichsupport the galvanometer coil and also provide the spring follow-up areimportant in obtaining maximum accuracy and sturdiness. This particularshape of stylus has additional characteristics which are apparent byexamining the typical electrocardiogram of Figure 2 which will now bedescribed.

The chart paper 4 has closely spaced longitudinal lines 80 which arespaced apart a distance of one millimeter equal to one-tenth of onemillivolt when the instrument is properly calibrated, and every fifthline 82 is heavier so that the distance between the heavy linesrepresents one-half of a millivolt. The transverse lines are some- 6what similar and comprise closelyspaced light lines 84 with everyfifthline 86 being heavy, and the paper is moved at a predetermined speed sothat these lines represent time with thev space between adjacent linesrepresenting one twenty-fifth of a second and the space between theheavy lines representing one-fifth of a second.

The electrocardiogram 87 of Figure 2 comprises light portions 88 andheavy portions 90; the light portions are produced by stylus 10 movingtransversely of the paper i. e., substantially parallel to lines 84 and86, while the heavy portions 90 are produced by the paper moving whilethe stylus is relatively stationary. As will be best under stood byreferring to Figure 1, the stylus 10 moves tangentially of its curvedcontact surface when it moves across the paper and it moves at a veryrapid rate. On the other hand, the paper moves somewhat parallel to thecenter of curvature of the curved contact surface of the stylus so thatwhen the stylus is stationary there is a endency for the record line tobe widened by the heating effect of the portions of the stylus at thetwo sides (Figure 4;). of the pointed contact; and this tendency for theline to be widened is emphasized by the relatively slow movement of thepaper, that is, paper moves past the stylus at a sufliciently slow rateto, permit the stylus to make a line of the width shown at 90. Thevariations in the width of line between the light portions 88 and theheavy portions 90 result from varied rate of movement of the stylus.This difference in the weight of the lines corresponds exactly to thedifference in the weight of lines on an electrocardiogram produced bythe well known standard string galvanorneter type electrocardiograph.Therefore, an electrocardiogram such as that of Figure 2, produced onthe instrument herein disclosed, is similar in these characteristics tothose produced on the prior standard instruments, with which physiciansand technicians are familiar, and may be interpreted with reference tothe more or less classical examples of electrocardiograms which appearin medical literature.

Ithas been pointed out above that case may be released at its forwardend and lifted from the base plate and this raises the stylus and boomaway from the paper and platen assembly. When the case is swung back soas to return it to the position shown, the stylus may engage the paperinitially with very light pressure, but when the case is clamped downand the galvanometer unit is moved to its position wherein the axis ofthe galvanometer coil coincides exactly with that of the axis of surface20, this final positioning movement tends to stress or tension the boomand the stylus is then pressed against the paper with the desiredpressure. While the boom is not deformable in its longitudinaldirection, it has sufiicient flexibility to permit this tensioningaction and the stylus is held resiliently against the recording surface.

The strip 26 of aluminum beneath lip 24 and the Zone within which thestylus contacts the paper insures that the stylus will not beoverheated, and the platen will not be damaged. During normal operationthe stylus contacts the record paper with the paper riding somewhat inair, that is, it is supported by the platen surface 20 and is heldslightly above the upper surface of the strip 26 with the result thatthe recording action of the heated stylus is not interfered with by thestrip conducting the heat away from the stylus. However, if the papersupply should become exhausted without the operator being aware of thatfact, the stylus drops onto strip 26 and the heat of the stylus isconducted'therefrom by the strip and this keeps the stylus temperaturewithin acceptable and safe limits. Furthermore, the strip will withstandrelatively high temperatures without injury.

In this embodiment the heating current to the stylus is turned off whenthe paper feeding operation stops. Furthermore, the heating current andthe coil deflecting current circuits are disconnected when thegalvanometer is lifted by swinging case 70 on hinge 72.

As various embodiments may be made of the above invention and as changesmight be made in the embodiment above set forth,-it is to be understoodthat all matter hereinbefore set forth or shown in the accompanyingdrawings is to be interpreted as illustrative and not in a limitingsense. I

I claim:

1. In an electrocardiograph of the type having a galvanometer unit,- astylus assembly associated therewith, and a record chart and platenassembly adapted to form the record chart into a curved surface havingits axis coincident with the axis of rotation of the stylus assembly,the combination of a coil in said galvanometer unit adapted to berotated about a predetermined axis, an electrically heated styluselement and a boom secured to said stylus element and said coilincluding electrical circuit connections for said element and mountingmeans for said galvanometer coil comprising a plurality of spring stripseach of which has a curved central portion with one end fixed to thecoil and the other end fixed to the stationary frame of the instrumentand arranged to provide both mechanical support and electricalconnection for said coil and stylus assembly.

2. An instrument as described in claim 1 wherein said mounting meanscomprises four of said springs individually mounted in pairs at oppositeends of said coil, one of said pair providing electrical connections tosaid stylus assembly and the other providing electrical connections tosaid coil. C

3. An instrument as described in claim 2 wherein said boom comprises twotubular metal struts which have their ends adjacent each other wherethey are attached to said heated stylus element, the opposite ends ofsaid struts being spaced from each other and supported by the coiladjacent and electrically connected to the springs providing theelectrical circuit to and from said heated element.

4. In an electrocardiograph of the type having a galvanometer unit and arecord chart and platen assembly adapted to form the record chart into aportion of a cylindrical surface, the combination of a coil in saidgalvanometer unit adapted to turn about a predetermined axis, a stylusassembly comprising a'heated stylus element, a truss rigidly connectedat one end to said stylus element and rigidly fixed to said coil at theother end to form a stylus boom flexible in a first plane which islongitudinal of said truss and passes through the axis of said coil andis rigid in a second plane which is the plane of the truss and isperpendicular to said first plane whereby said stylus element preciselytracks the rotary movements of said coil but may flex to and from therecord chart surface, mounting means for said coil comprising aplurality of spring strips each having one end fixed to said coil andthe other end fixed to the stationary frame of the instrument andarranged to provide both mechanical support and electrical connectionfor said coil and stylus assembly.

5. A device as described in claim 4 wherein said stylus boom comprises apair of conducting members joined together in a gradually divergingmanner from said stylus element and a plurality of spaced insulatingmembers connecting said conducting members whereby the electricalheating circuit for said stylus element is down one conducting memberthrough the stylus element and back up the other conducting'membcr to apair of said spring strips.

6. A device as described in claim 5 wherein there are four of saidspring strips, each having an S curved cen tral portion, and one pair isconnected to provide electrical connection to said conducting membersand the other pair is connected to provide electrical connection to saidcoil.

7. An electrocardiograph instrument of the type having a galvanometerunit and a record chart and platen assembly positioned to form therecord chart into a portion of a cylindrical surface, comprising a'coilin said galvanometer unit, a stylus assembly operatively connected tosaid coil at one end and carrying at its other end a stylus mounted tocontact said record chart, supporting means for said coil comprising aplurality of spring strips each having one end'thereof fixed to'saidcoil and the other end thereof fixed to the stationary frame portion ofthe instrument and arranged to aid in the support of said coil in apredetermined central position with respect to said pivots wherebysignals of equal magnitude but opposite polarity will produce equal butoppositely directed deflections of said stylus element.

3. A device as described in claim 7 wherein said stylus assembly isrigidly fixed to said coil and said supporting means comprises fourspring clips having an S curved central portion and one pair isconnected to provide the electrical connection for said stylus and theother pair is connected to provide the electrical connection forsaidcoil. l

9. A device as described in claim 8 wherein the platen assembly includesa canopy portion of magnetic material extending upwardly between saidstylus boom and said galvanometer unit and shielding said boom andpreventing damping of the deflections.

10. An electrocardiograph of the type having a galvanometer unit and arecord chart and platen assembly mounted to form the record chart into aportion of a cylindrical surface, the combination of a' magnetic corestructure comprising a pair of oppositely disposed pole pieces havingconcave pole faces, a stationary cylindrical core portion centrallypositioned between said pole pieces to form two equal arcuate gaps inthe magnetic circuit of said galvanometer unit; a rectangular coilloosely mounted about said stationary cylindrical element on a pair ofpivots so that the side portions of said coil are positioned in saidgaps; a stylus assembly comprising a heated stylus element and a stylusboom connected thereto at one end and rigidly mounted on said coil atthe other end; supporting means for said coil comprising a plurality ofspring strips having one end fixed to said coil and the other end fixedto the stationary frame portion of said instrument and arranged tomaintain said coil in a central position within said arcuate gaps tosubject each side of said coil to a uniform magnetic field whereby equaldeflections in either direction are obtained for signals of equalmagnitude.

ll. In a direct-writing electrocardiograph, a writing assembly includingmeans for producing a magnetic field, a coil positioned within the fieldand having an axis of rotation, resilient means for supporting the coilfor partial rotation within the field an about said axis including fourstrips of resilient material mechanically connected to said coil atspaced points around its periphery and in pairs with two of said pointsbeing spaced from said axis on one side of said coil and the other twopoints being spaced from said axis on the other side of said coil, astylus-supporting boom mechanically coupled to said coil at two pointsspaced from the axis of rotation of said coil, and stylus means carriedby said boom.

12. Au electrocardiograph writing mechanism comprising a permanentmagnet having pole pieces with spaced opposing arcuate surfaces, a coilform of generally rectangular cross section positioned between said polepieces, four S-shaped coil-supporting members formed of beryllium copperstrips each secured at one end to said coil form, two of said membersbeing secured at spaced points to one end of the coil form and the othertwo at spaced points to the opposite end of the coil form, frame meanssupporting the other ends of said members, a coil extending around andcarried by said coil form, two metal boom-supporting strips secured totwo of said coil-supporting members immediately adjacent said coil andextending outwardly in opposite directions, a generallyV- shapedstylus-supporting boom having two converging legs each joined at thebase of the V to one of said boomsupporting. strips, stylus meanscarried by said bo'om at the apex of the V, and chart-supporting meansadjacent said stylus means for supporting a moving chart strip.

13. In an electrocardiogranh for producing directly a visible trace on achart strip, apparatus comprising a frame, a Writing assembly swingablysecured to said frame and including means for producing a magneticfield, coil movably supported in said field, and stylus meansmechanically secured to and extending from said coil, chart positioningmeans for guiding and positioning said chart strip with respect to saidstylus means near the region engaged by said stylus means, meanssupporting said chart-positioning means on said frame and permittinglimited relative movement between said frame and said chart-positioningmeans, and means rigidly secured to said writing assembly and arrangedto releasably engage said chart-positioning means and hold it inpredetermined fixed position relative to said writing assembly. 14. Inan electrocardiograph for making a visible trace on a chart strip,apparatus comprising a base, a writing assembly including meansproducing a magnetic field, 2

a movable coil positioned in said field, and stylus means mechanicallycoupled to said coil and arranged to be deflected by movement of thecoil, a platen secured to said base for supporting said chart strip,said platen being arranged for limited freedom of movement with respectto said base, supporting means secured to said writing assembly andswingabiy secured to said base and movable between a closed positionwherein said stylus means is positioned near the platen and an openposition wherein the stylus means is removed from the proximity of saidplaten, and positioning means on said writing assembly arranged toengage and position said platen relative to said writing assembly whensaid supporting means is in its closed position.

15. In an electrocardiograph for making a visible trace on a chartstrip, apparatus comprising a base, a writing assembly including meansproducing a magnetic field, a movable coil positioned in said field, andstylus means mechanically coupled to said coil and arranged to bedeflected by movement of the coil, chart positioning means forpositioning said chart strip adjacent said stylus means, meanssupporting said chart-positioning means for limited movement withrespect to said base, resilient means urging said chart-positioningmeans toward a predetermined position, supporting means secured to saidwriting assembly and swingably secured to said base and movable betweena closed position wherein said stylus means is positioned near theplaten and an open position wherein the stylus means is removed from theproximity of said platen, and means on said cover engaging saidchart-positioning means and moving it against the force of saidresilient means when said supporting means is in its closed positionthereby to position said stylus means precisely with respect to saidchart strip.

16. Electrocardiograph apparatus for producing a visible trace on achart strip comprising a base, a cover swingably mounted on said baseand movable between open and closed positions, a writing assemblysecured to said cover and including a permanent magnet having polepieces with spaced opposing arcuate surfaces, a coil form of generallyrectangular cross section positioned between said pole pieces, fourS-shaped coil-supporting members formed of beryllium copper strips eachsecured at one end to said coil form, two of said members being securedat spaced points to one end of the coil form and the other two to spacedpoints at the opposite end of the coil form, frame means supporting theother ends of said members, a coil extending around and carried by saidcoil form, two metal boom-supporting strips secured to two of saidcoil-supporting members immediately adjacent said coil and extendingoutwardly in opposite directions, a generally V-shaped stylus-supportingboom having two diverging legs each joined at the base of the V to oneof said boom-supporting strips, and stylus means carried by said boom atthe apex of the V, and chart-supporting means on said base forsupporting said chart strip adjacent the stylus means when the cover isin its closed position.

17. Electrocardiograph apparatus for producing a visible trace on achart strip comprising a base, a cover swingably mounted on said baseand movable between open and closed positions, a writing assemblysupported by said cover and including a permanent magnet having polepieces with spaced opposing arcuate surfaces, a coil form of generallyrectangular cross section positioned between said pole pieces, fourS-shaped coil-supporting members formed of beryllium copper strips eachsecured at one end to said coil form, two of said members being securedat spaced points to one end of the coil form and the other two to spacedpoints at the opposite end of the coil form, frame means supporting theother ends of said members, a coil extending around and carried by saidcoil form, two metal boom-supporting strips secured to tWo of saidcoil-supporting members immediately adjacent said coil and extendingoutwardly in opposite directions, a generally V-shaped stylus-supportingboom having two diverging legs each joined at the base of the V to oneof said boom-supporting strips, and stylus means carried by said boom atthe apex of the V, chartsupporting means on said base for supportingsaid chart strip, adjacent said stylus when the cover is in its closedposition and including a lower platen movably supported by said base,and means on said cover arranged to engage said platen for positioningsaid platen accurately with respect to said writing assembly when thecover is in its closed position.

1.8. In an electrocardiograph for producing directly a Visible trace ona chart strip, apparatus comprising a frame, a Writing assemblyswingably secured to said frame and including means for producing amagnetic field, a coil movably supported in said field, and stylus meansmechanically secured to and extending from said coil, said stylus meansbeing heated, chart positioning means for guiding and positioning saidchart strip with respect to said stylus means near the region engaged bysaid stylus means, means supporting said chart-positioning means on saidframe and permitting limited relative movement between said frame andsaid chart-positioning means, and means rigidly secured to said writingassembly and arranged to releasably engage said chart-positioning meansand hold it in predetermined fixed position relative to said writingassembly, said chart positioning means containing a strip of metal ofhigh heat conductivity opposite the place on said chart engaged by saidheated stylus means.

19. In an electrocardiograph, apparatus as claimed in claim 18 andwherein the surface of said metal strip is spaced slightly below thesurface of the chart positioning means.

References Cited in the file of this patent UNITED STATES PATENTS1,071,192 Von Voss Aug. 26, 1913 1,782,519 Sutton Nov. 25, 19301,901,921 Means Mar. 21, 1933 2,003,913 Wente June 4, 1935 2,412,639Traugott Dec. 17, 1946 2,606,093 Reason Aug. 5, 1952 FOREIGN PATENTS612,619 Great Britain Nov. 16, 1948

